Astaxanthin over-producing strains of phaffia rhodozyma

ABSTRACT

Phaffia rhodozyma strains are described which produce greater than 3,000 ppm astaxanthin based on dry yeast solids when cultivated in a volume of nutrient medium of at least about 1,500 liters and containing in excess of 4 percent, preferably in excess of 6 percent, dry yeast solids. These and other strains are cultivated by an improved fermentation method comprising extending the maturation phase of the fermentation by one or more various techniques including exposing the yeast cells to a low-intensity light, slow feeding the cells with a rapidly metabolized energy source, e.g. glucose, and replacing the rapidly metabolized energy source with a slowly metabolized energy source, e.g. gylcerol. The cells of these strains are incorporated into animal feeds, particularly feeds for salmonid fishes, to impart or enhance the red pigmentation of these animals and products made from these animals.

BACKGROUND OF THE INVENTION

This invention relates to astaxanthin. In one aspect, the inventionrelates to astaxanthin produced by yeast cells while in another aspect,the invention relates to methods of producing and cultivating mutantstrains of Phaffia rhodozyma yeast cells that produce astaxanthin inexcess of the typical Phaffia rhodozyma yeast cell found in nature. Inyet another aspect, the invention relates to using products made fromthese yeast cells as a dietary supplement in various animal feeds.

A distinct red color is of prime importance to customer acceptance ofcertain food products, particularly aquatic food animals such as salmon,sea bream, trout, shrimp, lobster and many other marine animals. Theoxygenated carotenoid astaxanthin(3,3'-dihydroxy-β,β-carotene-4,4'-dione) is responsible for the redcolor of these aquatic animals. In addition to being responsible for thecharacteristic color of these animals, astaxanthin plays a criticalnutritional role in the life of these marine animals (Torrissen, 1989.Proc. Third Int. Symp. on Feeding and Nutr. in Fish, Toba Aug. 28-Sep.1, Japan, pp. 387-399, Meyers and Chen, 1982. World Aquaculture Society,Special Publication No. 3, pp. 153-165). These references areincorporated herein by reference. This carotenoid is also useful foradding pigmentation to the flesh and products of other animals, and toother foodstuffs, e.g. poultry and eggs, various dairy products, snackfoods, and the like.

Astaxanthin is the most abundant carotenoid present in the aquaticworld. Aquatic animals, like terrestrial animals, generally cannotsynthesize astaxanthin or any other carotenoid, although many of theseanimals accumulate carotenoid compounds that are present in their diets.Some of these animals, such as crustaceans, can interconvert somecarotenes to oxygenated forms of carotenoids (called xanthophylls) ofwhich astaxanthin is the predominant compound formed. However, salmonidfishes and red sea bream accumulate dietary astaxanthin even thoughthese fish cannot convert any other carotenoid compound to astaxanthin.Therefore, the astaxanthin present in salmonid and sea bream fish, andin products produced from these fish, must be derived directly fromdietary sources.

Plants, including marine microalgae and special yeasts such as Phaffiarhodozyma, are the primary source of carotenoid compounds in the world.As noted above, carotenoids are not biosynthesized de novo by animals.However, animals in general require certain carotenoids from which theybenefit directly or indirectly, and these carotenoids are obtained fromdietary sources. Examples of substances essential to most animals thatare derived from certain carotenoids are vitamin A and rhodopsin. In themarine world, animals that are low on the food chain, such ascrustaceans, eat microalgae and other carotenoid containing organismsfrom the plant world, and convert the carotenoid compounds present inlarge part to astaxanthin by natural metabolic processes. Theastaxanthin is then stored in the body of these astaxanthin producinganimals.

Wild grown salmonid fishes and red sea bream obtain their astaxanthinfrom the crustaceans and other astaxanthin containing organisms thatmake up an important part of their diet. In the case of pen-grownsalmonids and red sea bream, the feeds used to produce these fish mustbe supplemented with astaxanthin in order to provide a dietary source ofthis important natural constituent of these fishes. Currently, syntheticastaxanthin is added to feeds prepared for production of salmonids andred sea bream in aquaculture to provide a source of this carotenoidcompound. In some cases, synthetic canthaxanthin (an oxygenatedcarotenoid compound that is very closely related to astaxanthin) is usedin place of astaxanthin in feeds for salmonids and red sea bream, butthis compound does not function as well in these fishes as the naturallypredominant astaxanthin.

Natural sources of dietary astaxanthin are in great demand by theaquacultural industries. Natural sources of dietary carotenoids thathave been investigated for farmed fish include krill, crawfish,crustacean processing by-products, algae and higher plants. However,these natural sources tend to be too expensive and of limitedavailability and reliability to be commercially viable.

The red yeast, Phaffia rhodozyma, has received great attention fromindustry as a natural source of astaxanthin since it was isolated fromtree sap, and the red color identified as astaxanthin (Miller, Yoneyamaand Soneda. 1976. Int. J. Syst. Bacteriol. 26: 286-291, Andrewes, Phaffand Starr. 1976. Phytochem. 15: 1003-1007) Phaffia rhodozyma was firstdemonstrated to pigment salmonid fishes in 1977 (Johnson, Conklin andLewis. 1977. J. Fish. Res. Board. Can. 34: 2417-2421, Johnson, Villa andLewis. 1980. Aquaculture. 20: 123-134). The potential advantages ofPhaffia rhodozyma as a source of carotenoid pigments for aquaculture arethat it is a natural product rich in essential nutrients (e.g. protein,lipids and B-vitamins) and that it contains astaxanthin (Johnson, Villaand Lewis. 1980. Aquaculture. 20: 123-134). However, natural isolates ofPhaffia rhodozyma produce so little astaxanthin (typically 100 to 300parts per million (ppm)) that they are not practical or economicalpigment sources for aquaculture (Torrissen, Hardy and Shearer. 1989.Reviews in Aquatic Science 1: 209-225, Johnson and An. 1991. CRC Crit.Rev. Biotech. 11: 297-326). If Phaffia strains are to be an economicallyfeasible feed additive for coloring aquatic animals, or any otherpotential foodstuff (animal or otherwise), then astaxanthinover-producing strains must be developed. Each of the references citedin this paragraph are incorporated herein by reference.

Mutants of naturally occurring "wild-type" Phaffia have been describedin the literature, allegedly capable of generating higher levels ofastaxanthin than the wild-type yeasts (International Publication No. WO88/08025 (International Application No. PCT/DK88/00068); EPO PublicationNo. 0 438 182 A1 (EPO Application No. 91900682.3); EPO Publication No. 0454 024 A2 (EPO Application No. 91106436.8); International PublicationNo. WO 91/02060 (International Application No. PCT/US90/00558); EPOPublication No. 0 474 347 A1 (EPO Application No. 91306489.5); and EPOPublication No. 0 427 405 A1 (EPO Application No. 90311254.8), all ofwhich are incorporated herein by reference). These strains reportedlyproduce higher levels of astaxanthin than the wild-type isolates underspecific conditions. However, these mutant strains produce higher levelsof astaxanthin only at relatively low biomass concentrations. Atrelatively high biomass concentrations, these mutant strains produceonly low levels of astaxanthin which are not high enough to bepractical.

Thus far, none of the reported Phaffia strains are capable of producingastaxanthin efficiently enough to compete economically with syntheticastaxanthin. Commercially viable strains have to produce astaxanthin atsubstantially higher levels than strains reported in the literature. Todevelop an economically viable astaxanthin production process, a strainshould produce in excess of 3,000 ppm, preferably in excess of 4,000ppm, astaxanthin based on dry yeast solids at more than 4 wt %,preferably more than 6 wt %, dry yeast solids (dys) in a large volume ofnutrient medium, e.g. 1,500 liters (1) or more. As here used, "wt % dryyeast solids" or simply "dry yeast solids" are washed solids determinedby the method described in Official Method of Analysis, A.O.A.C. 14thEdition (1984) Sections 10.215-10.225, which is incorporated herein byreference.

Besides the need to develop a suitable strain of Phaffia rhodozyma forcommercial astaxanthin production, methods for cultivating Phaffiarhodozyma also need to be developed which maximize astaxanthinproduction in large fermentors. Only limited literature sources areavailable dealing with the growth of Phaffia and production processes ofastaxanthin in large fermentors (International Publication No. WO88/08025 (International Application No. PCT/DK88/00068), and EPOPublication No. 0 454 024 A2 (EPO Application No. 91106436.8) both ofwhich are incorporated herein by reference). These reported fermentationprocesses give significantly lower yeast solids and astaxanthin levelsthan that required for an economically viable commercial scalefermentation process.

Not only do the various elements of producing astaxanthin from yeastcells require improvement, but so do the elements of astaxanthinabsorption and deposition in animal flesh and animal products.Carotenoid absorption and deposition in fish are affected by variousfactors: genetics, size, age, sex, duration of pigment feeding,environmental factors, and diet composition (Torrissen, Hardy andShearer: 1989: Reviews in Aquatic Science, 1: 209-225, which isincorporated herein by reference).

Various reports are available concerning the formulation of Phaffia orcarotenoid products (International Publication No. WO 88/08025(International Application No. PCT/DK88/00068), EPO Publication No. 0474 347 A1 (EPO Application No. 91306489.5), EPO Publication No. 0 454024 A2 (EPO Application No. 91106436.8), and Japanese PatentApplications 57-206342, 2238855 and 90 JP-285090 are exemplary, all ofwhich are incorporated herein by reference). In these reports, Phaffiaproducts were formulated in order to protect the pigments during dryingas well as during subsequent processing into fish feed. Variousantioxidants and stabilizers were added to Phaffia preparations forthose purposes.

The body temperature of salmonid fishes is equal to the temperature ofthe water in which they inhabit, e.g. generally 0 to 14 degreesCentigrade (C.). This means that the body temperature of these fishescan be, and occasionally is, lower than 10 C. Astaxanthin in Phaffia isconcentrated in oil droplets . Phaffia oil contains about 13% palmiticacid (16:00) with a melting point of 64 C., and about 32% oleic acid(18:1n9) with a melting point of 16 C. Because of these high meltingpoint fatty acids, Phaffia oil solidifies near 10 C. This makes itdifficult for fishes to incorporate Phaffia astaxanthin at watertemperatures below 10 C. at which Phaffia oil is solidified.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, we have developed andisolated novel strains of Phaffia rhodozyma which produce greater than3,000 ppm, often more than 4,000 ppm, astaxanthin based on dry yeastsolids at more than 4 wt %, often more than 6 wt %, dry yeast solidswhen grown under suitable conditions and in a working volume of nutrientmedia of at least about 1,500 l. These Phaffia strains can produceastaxanthin economically on a commercial production scale for theaquacultural and food industries. Certain of these Phaffia strains weredeposited with the American Type Culture Collection of Rockville, Md.,on Apr. 6, 1993 under numbers ATCC-74218 (UBV-AX1), ATCC-74219(UBV-AX2), ATCC-74220 (UBV-AX3), and ATCC-74221 (UBV-AX4).

In another embodiment of this invention, we have discovered methods forthe cultivation of Phaffia rhodozyma cells which produce high yeastsolids and high levels of astaxanthin. Generally, these methods includeproviding special fermentation conditions that promote the growth of theorganism in terms of an increase in cell numbers during a growth phase,and in terms of an enhanced and steady accumulation of astaxanthin inthe cells during a maturation phase. More specifically, these methodsinclude exposing the yeast cells during the growth and maturation phasesof fermentation to a source of light, and/or extending and stimulatingthe astaxanthin formation during the maturation phase by controlling thefeed rate of fermentable sugar, e.g. glucose, or by providing the yeastcells with energy sources that are slowly metabolized, e.g. glycerol.

In another embodiment of this invention, we have discovered that thePhaffia strains of this invention need not be disrupted to makeastaxanthin available to salmonids, sea bream, crustaceans, and otheranimals. Astaxanthin in undisrupted cells is more stable during drying,storage and feed preparation processes.

In yet another embodiment of this invention, we have discovered that anovel formulation of Phaffia product increases the astaxanthindeposition in fishes. This formulation is a blend of undisrupted Phaffiacells, vegetable oil or a blend of vegetable oils with a lowsolidification point, an emulsifier, and an antioxidant.

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request and payment of the necessaryfee.

FIG. 1 describes the genetic history of three of the Phaffia mutantstrains of this invention.

FIGS. 2-9 are photomicrographs showing the appearance of various mutantstrains.

FIG. 10 describes the weight gain of rainbow trout over the course of afeeding trial.

FIG. 11 describes the pigmentation of rainbow trout over the course ofthe same feeding trial as that of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

Mutagenesis

Astaxanthin over-producing yeast strains can be obtained by consecutivemutagenesis followed by suitable selection of mutant strains whichdemonstrate superior astaxanthin production. Preferably, the yeast cellsare of the genus Phaffia, and more preferably of the species Phaffiarhodozyma. Starting wild type yeast cell strains include those ondeposit with the various culture collections throughout the world, e.gthe ATCC and the Centraalbureau voor Schimmelcultures (CBS). Typicallyit is necessary to perform two or more consecutive rounds of mutagenesisto obtain desirable mutant strains.

Any chemical or nonchemical (e.g. ultraviolet (UV) radiation) agentcapable of inducing genetic change to the yeast cell can be used as themutagen. These agents can be used alone or in combination with oneanother, and the chemical agents can be used neat or with a solvent.

In those mutagenesis protocols employing a chemical mutagen, typicallythe mutagen is introduced into a buffered volume of cells, thoroughlymixed, and then the tubes are incubated at room temperature for 1 to 12hours (hr) with continuous gentle agitation. After the incubation, thereaction mixture is plated directly onto agar medium plates. Thecomposition of the agar can vary, but typically the composition includesglucose (or other carbon source), yeast extracts (such as thoseavailable from Universal Foods Corporation), agar, and a screening agentthat inhibits pigment formation and/or cell growth. The cells aredistributed evenly across the agar surface, usually by shaking withsterile 5 millimeter (mm) glass beads. The plates are then inverted andincubated at about 21 C. for 6-10 days under illumination which ispreferably a continuous low-intensity light. Similar growing techniquesare employed for those mutagenesis protocols in which the mutagen is anonchemical.

Screening for High Astaxanthin-Producing Mutants

Initial Screening on Plates and in Shake Flasks

After the incubation period, those yeast colonies that appear betterpigmented to the human eye than the mutagenized parent strain arecollected and subcultured onto new agar plates (often of the samecomposition as those used to grow the mutagenized parent strain). Afteran additional incubation period of 6-10 days under like conditions, thenew isolates that continue to be heavily pigmented are inoculated intoflasks, e.g. 50 ml flasks containing 10 ml of a blend of glucose andyeast extract. The isolates are then typically incubated for another6-10 days under similar conditions to the previous incubations but thistime on a shaker operating at about 200 revolutions per minute (rpm).After this incubation period, an aliquot (e.g. 0.2 ml) is taken and thetotal carotenoid content and astaxanthin content determined. Thosestrains exhibiting enhanced astaxanthin producing capabilities arecandidates for additional screening in a small batch fermentation, andare typically stored by freezing in an appropriate medium, e.g. 15 vol %glycerol at minus 80 C., until required for the next mutagenesis orscreening. This storage technique can be used after any of the screeningsteps or for simply maintaining production strains.

Screening in a Small Batch Fermentation

Following selection of appropriate astaxanthin producing mutants at the50 ml flask level, mutants are then usually screened for performance in2 l fermentors (e.g. Omni-Culture Fermentors, Virtis Corp., Gardiner,N.Y.) containing approximately 1.5 l of nutrient medium. In a typicalscreening procedure at this level, 250 ml flasks containing 30 ml of ablend of glucose and yeast extract are each inoculated with 100-250 μlof mutant yeast cells taken from a frozen stock of the strain of yeastcells that is to be tested. These flasks are then shaken at 200 rpm at20-22 C. under continuous light for 3 days. Aliquots of these cellcultures (15-20 ml) are then used to inoculate into the fermentors.

The working volume in these 2 l fermentors is usually 1.5 l of anenriched glucose yeast extract medium supplemented with various vitaminsand minerals in assimilable form. Typical of these vitamins and mineralsare ammonium sulfate, potassium phosphate, magnesium sulfate, zincsulfate, ferric ammonium sulfate, copper sulfate, inositol, pyridoxinehydrochloride, thiamine, calcium pantothenate, biotin, and the like. Thecombinations and concentrations of these materials, including theglucose and yeast extracts, can vary to convenience. If desired, anantifoam agent and/or other additives can also be incorporated into orused with the medium.

The fermentor with its medium is sterilized by autoclaving. The pH ofthe media is usually maintained between 4.5 and 7, and the temperaturebetween 15-24 C. The medium is usually sparged with filter sterilizedair (e.g. 2 liters per minute (l/min)), and it is continuously agitated(e.g. 700 rpm). Fermentations typically last 4-6 days, and they aresampled periodically for cell growth and astaxanthin production. Strainsshowing appropriate levels of growth and astaxanthin production arecandidates for screening at the fed-batch fermentation level.

Screening in a Fed-Batch Fermentation

Following identification of astaxanthin over-producing mutants in smallbatch fermentations, mutants are further screened for fast growth rate,high solids production and high astaxanthin production levels in 14 l,20 l, 250 l and 2,000 l fermentors. Typically, strains are propagated infermentors over a pH range of about 4.5 to 7 controlled with aqueousammonia, sodium hydroxide or both at a temperature range of 15 to 24 C.Agitation and aeration are adjusted as necessary to maintain desiredgrowth rates. The media with which the fermentors are charged arecompositionally similar to those used in the small fermentors, i.e. theycontain glucose (or other suitable carbon source), yeast extracts,vitamins, minerals and other additives, all in assimilable form,although the exact recipe may and probably will vary from that used forthe small fermentors. Antifoam agents and other processing aids can beused as desired.

The culture can be conducted as a batch fermentation until a desiredcell density is obtained, or the glucose (or other suitable carbonsource) supply can be started immediately. This supply is adjusted asnecessary to obtain the best yeast growth rate and astaxanthinproduction. Additional nitrogen can be supplied to the fermentation inthe form of ammonia or urea.

Cultivation of Phaffia rhodozyma

The Phaffia strains of this invention initially show rapid growth whichgradually slows as they approach a high cell concentration, e.g. greaterthan 6 wt % biomass solids. In a typical fermentation, the rate ofastaxanthin formation is initially slower than the growth rate of thePhaffia cells, but ultimately (during the later phase of thefermentation) the rate of astaxanthin formation exceeds the cell growthrate. We have termed this later phase the "maturation phase". We havefound that the rate of astaxanthin production is highest during theearly stages of the maturation phase.

In order to obtain better astaxanthin-producing fermentations, we havedeveloped three approaches to sustain or enhance the high rate ofastaxanthin production that occurs during the early stages of thematuration phase. During this enhanced maturation phase, the astaxanthinconcentration is increased over the standard maturation phase by atleast 2-fold, often 3-fold or more. The first technique is to expose theyeast cells to a light source, preferably a continuous, low-intensitylight, during the maturation phase, particularly from its inception tothat point in the phase at which the rate of astaxanthin productionbegins to significantly decline.

An and Johnson (Antonie van Leeuwenhoek. 1991. 57: 191-203, which isincorporated herein by reference) indicated that high intensity lightinhibits the growth and carotenoid production by Phaffia. Evans, et al.(EPO Publication No. 0 427 405 A1, EPO Application No. 90311254.8)indicate that Phaffia strains do better in daylight than in darkness.Both studies used Phaffia grown on agar plates. Like An and Johnson, wefound that continuous fluorescent light (regular lab lighting) reducedpigment yields of Phaffia in shake flasks, and like Evans we founddarkness to be inhibitory of carotenoid development in some Phaffiastrains. However, we also found that a low-intensity, preferablycontinuous, fluorescent light, i.e, less than about 100, preferably lessthan about 25 watts per kiloliter fermentation broth, actually promotescarotenoid production in some Phaffia strains grown in liquid media.These strains include those on deposit with the American Type CultureCollection bearing numbers ATCC-74218, ATCC-74219, ATCC-74220 andATCC-74221. We have also found that better astaxanthin production isobtained when these strains are provided with such a source of lightduring fed-batch fermentation. The light is not limited to anyparticular wavelength, but light of 250 to 700 nm, particularly visiblelight, is preferred. In those circumstances in which the fermentor isconstructed of metal or another opaque material, the light can be madeavailable through one or more glass (or similarly translucent material)ports while the nutrient medium containing the yeast cells iscontinually circulated past the port(s). Fermentation broth can also bepumped in a return circuit through a light transparent tube and returnedto the fermentor. In both these cases a high-intensity light, e.g. alight that delivers more than 15 w/kl can be used since only arelatively small surface area is exposed to the light.

Second, the yeast cells are provided with a controlled amount of arapidly, relative to a polysaccharide, metabolized energy source, e.g.glucose or sucrose. During the growth phase, the yeast cells are fedthis energy source, typically glucose, as rapidly as possible with theproviso that it does not accumulate in the nutrient medium to anysubstantial extent. This rate will vary with the yeast cell strain, thecomposition of the nutrient medium, the fermentation protocol, andsimilar factors. The accumulation of the energy source in the medium isgenerally a signal that the growth phase is ending and the maturationphase is beginning.

After the desired yeast solids is achieved and prior to the accumulationof the energy source, the feed rate of the energy source is reduced toat least about 50%, preferably at least about 40%, more preferably atleast about 30%, of the maximum feed rate during the growth phase.During this period of reduced energy source feed, the yeast cellscontinue to produce astaxanthin, but the growth in the number of yeastcells, i.e. the growth in the cell density, is restricted. This periodis allowed to continue until the cells no longer produce astaxanthin atan economically desirable rate.

To maximize the accumulation of astaxanthin during the maturation phase,the energy source feed rate can be reduced in a step-wise or continuousmanner. For example, with the onset of the maturation phase, the energysource feed rate can be reduced by 50% and after a certain period oftime, typically 12 to 24 hours, it can be reduced another 50%.

The third technique is to feed the yeast cells a slowly, relative toglucose, metabolized energy source during the growth and/or maturationphases. These energy sources or maturation extenders include mostmaterials that can be slowly metabolized by a yeast cell. Glycerol;polymerized forms of glucose, sucrose, and other polysaccharidestypically found in molasses and certain corn syrups; various alcoholssuch as methanol, ethanol, etc.; and various organic acids such assuccinic, glutamic, maleic; etc., are exemplary of these extenders.

In one embodiment of this technique (and like the reduced energy sourcefeeding technique), these extenders are fed to the yeast cells at thetime energy source (e.g. glucose) accumulation is detected in thenutrient medium, and they are fed in an amount and in a manner such thatthe astaxanthin production of the cells continues at a desirable rate.As this astaxanthin production rate slows, the amount of extender fed tothe cells is reduced accordingly. The exact amounts and the rate ofextender fed will vary with the strain, fermentation protocol, and likeconsiderations.

In another embodiment of this technique, these slowly metabolizedextenders can be fed to the yeast cells during the growth phase as partof or in addition to the energy source feed. In this circumstance, theyeast cells will first deplete the rapidly metabolized energy source,e.g. glucose, and as their rate of consumption of this energy sourceslows, this signals that the growth phase is ending and the maturationphase is beginning. At this time, the addition of the energy source tothe nutrient medium is stopped and as the remaining rapidly metabolizedenergy source in the medium is exhausted, the yeast cells will begin tometabolize the remaining slowly metabolized energy sources. Theseremaining slowly metabolized energy sources can be supplemented, asdesired, with additional materials as described above.

The use of maturation extenders, in either format, will extend thisperiod in a manner similar to the other two extension techniques. Inaddition, these techniques can be used in any combination with oneanother, and typically the continuous light technique is used incombination with one of the feed techniques.

The early stages of the maturation phase continues until the astaxanthinproduction rate slows (as measured in the production of astaxanthin perunit volume per unit time, e.g. mg/l/hr). This usually occurs 2 to 4days after the end of the growth phase. The rate is, of course, acontinuum and at some point after it begins to decrease from themaximum, the early stages of this phase are over and continuation of thematuration phase becomes economically undesirable and it is terminated.

Yeast Cell Recovery and Product Preparation

Phaffia yeast is manufactured as a pure culture fermentation product.Fermentation raw materials are selected from a number of vendors basedon availability and suitability for the process. The major componentsfor the growth of Phaffia rhodozyma include high dextrose equivalent(DE) corn syrup (or equivalent source of fermentable sugars), yeastextract, ammonia, inorganic phosphates, and magnesium sulfate. Inaddition to these major components, a number of micronutrients, such astrace metals and vitamins, are required. All of these nutrients arecommonly used in commercial fermentation processes, including themanufacture of yeast for feed and food. Each component is optimized togenerate the maximum yield of Phaffia yeast astaxanthin. Foaming duringthe fermentation is controlled through the addition of food approveddefoaming agents.

The fermentation is conducted in pure culture fermentors which have beencleaned and sterilized prior to use. All nutrients added to thefermentors during the fermentation process are sterilized before use.

The production of Phaffia yeast described in this invention consists ofa fed-batch fermentation. Other fermentation techniques can be used ifdesired. The addition of nutrients during the fermentation is optimizedto achieve rapid production of both the Phaffia yeast biomass andastaxanthin.

During the fermentation a number of conditions are controlled andmaintained. These include the acidity of the medium, the fermentationtemperature, and the degree of aeration.

The fermentation is usually terminated when the astaxanthin productionfalls below a commercially desirable level, and it is terminatedtypically by transferring the culture (i.e. fermentation broth) from thefermentor by any conventional means to a refrigerated storage vessel toawait concentration by centrifugation or filtration. Continuouscentrifuges or filtration units are used for the preliminaryconcentration of the fermentation broth. The fermentation broth ispassed through these units, and the yeast concentrate (i.e. yeast cream)is transferred to a refrigerated yeast cream storage tank.

An edible antioxidant, such as ethoxyquin, vitamin E, butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), or ascorbylpalmitate; an edible oil such as a vegetable oil, e.g. corn oil,safflower oil, sunflower oil, soybean oil, etc.; and an edibleemulsifier, such as soy bean lecithin or sorbitan esters, can be addedto the yeast cream at this stage. As here used, "edible" means amaterial that is approved for human or animal consumption. This servesto protect the astaxanthin during processing and shipment and alsoimproves the pigment deposition in fish flesh.

The oil, emulsifier and antioxidant can be added at any convenient timeduring Phaffia yeast processing. In one embodiment, the oil, or blend ofoils, emulsifier(s), and one or more antioxidants, are blended with oneanother, and then the blend is mixed with the broth concentrate (yeastcream), dried, and packaged for shipping. In another embodiment, theoil, emulsifier and antioxidant are added to the yeast cream after ithas been dried. In yet another embodiment, one or two of the additivesare blended with the yeast cream prior to drying, while the remainingadditive(s) are blended with the yeast cream after it has been dried.The oil or blend of oils comprises between about 0.1 and 10 wt %, theemulsifier(s) between about 0.1 and 10 wt % and the antioxidant betweenabout 0.02 and 2 wt % based on the total weight of the final dryproduct.

Prior to drying, the cream is standardized to a suitable astaxanthincontent usually 3,000, 4,000 or 5,000 milligrams per kilogram of theproduct (mg/kg) through the addition of feed yeast (Yeaco^(tm) -20produced by Universal Foods Corporation or equivalent).

The standardized product is then dried by any suitable means, e.g. spraydrying, drum drying, etc., and eventually packaged, typically in either20 or 25 kg, heat-sealed, polylined boxes. The packaging is designed toprotect the product from light, oxygen, and moisture.

In one embodiment of this invention, the yeast cream is dried usingconventional equipment and techniques, such that a substantial number,preferably a substantial majority, of the cells are not disrupted by theprocess, i.e. such that the cells retain the bulk of their sphericalshape. We have found that unbroken yeast cells provide astaxanthin toconsuming animals as, or nearly as, efficiently as broken cells.

In another embodiment of this invention, the yeast cream is dried in amanner that promotes disruption of the cells such that most of the cellsin the dried product are broken or fragmented, i.e. the cells no longerretain their substantially spherical shape. If such broken cells aredesired and not provided by the drying process, then the cells can besubjected to a milling step or enzymatic treatment in which the cellsare broken.

The following examples are illustrative of certain specific embodimentsof this invention. Unless indicated to the contrary, all parts andpercentages are by weight.

SPECIFIC EMBODIMENTS

Pigment Extraction and Astaxanthin Analysis

Astaxanthin content is determined as reported by Sedmak, Weerasinghe andJolly in Jolly. 1990. Biotechnol. Techniques 4: 107-112, which isincorporated herein by reference.

Yeast cells are washed twice in 12×100 mm test tubes with 4 ml ofdeionized water. After washing and decanting the water, the test tubescontaining the washed cell pellets are inverted to drain the water. Theinsides of the tubes are then wiped with tissue paper to remove most ofthe water from the tube. To each tube is then added 0.5 ml of dimethylsulfoxide (DMSO) (Sigma Chemical Co., St. Louis, Mo.) preheated to 55 C.The tubes are vortex agitated for 20-30 seconds (sec) and 0.1 ml of0.02M sodium phosphate (pH 7.0) then is added to partition thecarotenoids into 1 ml of subsequently added organic solvent. Forcompatibility with high performance liquid chromatography (HPLC)analysis of astaxanthin, 1 ml of hexanes:ethyl acetate (50:50 volumebasis, HPLC grade) is used. The tubes are then vortex agitated for 30-40sec to mix the aqueous and organic phases. The phases are then separatedby centrifugation for 3 min in a desk-top clinical centrifuge. Theorganic phase is removed and the pigmented carotenoid content of theorganic phase determined from the absorbency at 480 nm (A₄₈₀). The totalcarotenoids are calculated using the extinction coefficient E₁ cm^(1%)=2,150 (based on determinations using authentic synthetic astaxanthin).

The astaxanthin content is then determined by HPLC. Samples for HPLCanalysis are diluted in hexanes:ethyl acetate (50:50 volume basis), andthen made to 0.1% acetic acid with glacial acetic acid and filteredprior to injection. The column is an Alltech (Deerfield, Ill.) Nucleosil100 silica 5 micron, 250×4.6 mm stainless steel column with an Alltechguard column. The eluting solvent is hexanes:ethyl acetate (50:50 volumebasis) without glacial acetic acid. The eluant is monitored at 476 nm.The percent astaxanthin is then calculated from the area under the curveat the position of a synthetic astaxanthin standard.

Astaxanthin concentration is then calculated as follows: ##EQU1##

EXAMPLE 1 Development of Mutant Strains

Phaffia rhodozyma mutants ATCC-74218 (UBV-AX1), ATCC-74219 (UBV-AX2),ATCC-74220 (UBV-AX3) and ATCC-74221 (UBV-AX4) were developed from wildtype strains by repeated mutagenesis as described in the sectionentitled Mutagenesis. FIG. 1 illustrates the genetic history of UBX-AX2,UBX-AX3 and UBV-AX4. UBV-AX1 was isolated after seven mutagenizations.

EXAMPLE 2 Cultivation of Novel Strains

The data in Tables 1, 2 and 3 demonstrate that the Phaffia strains ofthis invention grow to high levels of cell solids and produce highlevels of astaxanthin in working volumes of various sizes. In some ofthe literature, astaxanthin is not distinguished from total carotenoids,and thus the actual level of astaxanthin is considerably lower than thatreported. The astaxanthin values in the Tables below are based on HPLCquantifications of astaxanthin.

14 l Fermentation

About 30 g (dys basis) of actively growing culture in 1.5 l ofappropriate growth medium are inoculated into a 14 l Virticulturefermentor (Virtis Corporation, Gardiner, N.Y.). A typical formulationfor the set broth is:

    ______________________________________                                        INGREDIENT            AMOUNT (g)                                              ______________________________________                                        YEAST EXTRACT         75                                                      AMMONIUM SULFATE      25                                                      MONOBASIC POTASSIUM   15                                                      PHOSPHATE                                                                     MAGNESIUM SULFATE      5                                                      INOSITOL               0.65                                                   PYRIDOXINE             0.35                                                   ZINC SULFATE           0.15                                                   THIAMINE HYDROCHLORIDE                                                                               0.1                                                    CALCIUM PANTOTHENATE   0.08                                                   FERRIC AMMONIUM SULFATE                                                                              0.05                                                   CUPRIC SULFATE         0.01                                                   BIOTIN                 0.0005                                                 TAP WATER              5 l                                                    ANTIFOAM               5 ml                                                   pH                     5.5                                                    ______________________________________                                    

Start-up conditions are 8 standard liters per minute (SLPM) aeration and500 rpm agitation. The pH is controlled at 5.5 with 750 ml 1:3 dilutionof reagent grade ammonium hydroxide, NH₄ OH. Food grade antifoam isadded as required. The culture is fed 1750 g glucose (Cerelose™, CPCInternational, Summit-Argo, Ill.) as a 50% by weight solution at a ratesuch that the glucose concentration is less than 5 grams per liter(g/l), preferably between 0.1 and 2.5 g/l throughout the fermentation.Dissolved oxygen is controlled by agitation and airflow to between 20%and 90% saturation. Results of such fermentations with UBV-AX3 and 4 arepresented in Table 1:

                  TABLE 1                                                         ______________________________________                                        Astaxanthin Production in 14 l Fermentor                                                Time        Solids  Astaxanthin                                     Strain    (hrs)       (%)     (μg/g dys*)                                  ______________________________________                                        UBV-AX3   115         8.6     6660                                            UBV-AX4   115         7.7     4670                                            ______________________________________                                         *dys: Dry Yeast Solids                                                   

2000 l Fermentation

About 3.6 kg (dys basis) of actively growing culture in 120 l ofappropriate growth media are inoculated into a 2000 l IF2000 NewBrunswick Scientific fermentor (New Brunswick Scientific Corporation,Edison, N.J.) containing about 700 l of the broth described below:

    ______________________________________                                        INGREDIENT                AMOUNT                                              ______________________________________                                        YEAST EXTRACT             6      kg                                           MONOBASIC POTASSIUM PHOSPHATE                                                                           4      kg                                           MAGNESIUM SULFATE         4      kg                                           DEXTROSE                  3      kg                                           SODIUM CHLORIDE           700    g                                            FERROUS SULFATE           55     g                                            CALCIUM PANTOTHENATE      25     g                                            ZINC SULFATE              15     g                                            CITRIC ACID               5      g                                            MANGANOUS SULFATE         3      g                                            COPPER SULFATE            1      g                                            BIOTIN                    400    mg                                           COBALT SULFATE            300    mg                                           THIAMINE HYDROCHLORIDE    200    mg                                           BORIC ACID                80     mg                                           TAP WATER                 700    l                                            ANTIFOAM                  200    ml                                           pH                        5.5                                                 ______________________________________                                    

Start-up conditions are 700 SLPM aeration and 100 rpm agitation. The pHis controlled at 5.5 with anhydrous ammonia. Food grade antifoam isadded as required. The culture is fed 800 kg of a 45% by weight solutionof unrefined high dextrose corn syrup (Cargill Incorporated, Eddyville,Iowa) at a rate such that glucose does not accumulate in thefermentation broth to more than 5 g/l, preferably to 0.1-2.5 g/l.Dissolved oxygen is controlled by agitation and airflow to between 20%and 70% saturation. The volume of the broth upon termination of thefermentation is approximately 1,500 l. The results of such afermentation with UBV-AX2 are presented in Table 2.

                  TABLE 2                                                         ______________________________________                                        Astaxanthin Production in 2,000 l Fermentor                                             Time        Solids  Astaxanthin                                     Strain    (hrs)       (%)     (μg/g dys*)                                  ______________________________________                                        UBV-AX2   136         10.9    5321                                            ______________________________________                                         *Dry Yeast Solids                                                        

40,000 l Fermentation

About 160 kg (dys basis) of actively growing culture in 4,000 l ofappropriate growth media are inoculated into a 40,000 l fermentor. Atypical formulation for the set broth is:

    ______________________________________                                        INGREDIENT              AMOUNT (kg)                                           ______________________________________                                        YEAST EXTRACT              81                                                 MONOBASIC POTASSIUM        68                                                 PHOSPHATE                                                                     MONOBASIC SODIUM PHOSPHATE                                                                               14                                                 MAGNESIUM SULFATE          80                                                 DEXTROSE                   50                                                 FERROUS SULFATE            0.650                                              CALCIUM PANTOTHENATE       0.470                                              ZINC SULFATE               0.150                                              CITRIC ACID                0.060                                              MANGANOUS SULFATE          0.035                                              COPPER SULFATE             0.035                                              SODIUM MOLYBDATE           0.020                                              BIOTIN                     0.0035                                             COBALT SULFATE             0.0035                                             THIAMINE HYDROCHLORIDE     0.0018                                             BORIC ACID                 0.0023                                             TAP WATER               13,500                                                ANTIFOAM                   4 l                                                pH                         5.5                                                ______________________________________                                    

Start-up conditions are 8,000 SLPM aeration and 40 rpm agitation. The pHis controlled at 5.5 with anhydrous ammonia. Food grade antifoam isadded as required. The culture is fed 17,000 kg of a 42% by weightsolution of unrefined high dextrose corn syrup (Cargill Incorporated,Eddyville, Iowa) at a rate such that glucose does not accumulate in thefermentation broth to more than 5 g/l, preferably to 0.1-2.5 g/l.Dissolved oxygen is controlled by agitation and airflow between 20% and70% saturation. Results of such a fermentation with UBV-AX1 arepresented in Table 3:

                  TABLE 3                                                         ______________________________________                                        Astaxanthin Production in 40,000 l Fermentor                                            Time        Solids  Astaxanthin                                     Strain    (hrs)       (%)     (μg/g dys*)                                  ______________________________________                                        UBV-AX1   157         7.8     5060                                            ______________________________________                                         *Dry Yeast Solids                                                        

EXAMPLE 3 Strain Descriptions: Colony Morphology

Colony morphology of the novel strains were observed on 2-4 week oldstreak plates which contained 2% glucose, 0.5% Tastone^(tm) -154(Universal Foods Co. Yeast Extract) and 1.5% agar.

UBV-AX1: Well isolated colonies are 4-5 mm in diameter. Some colony sizeheterogeneity exists within the culture. Smaller colonies range in sizefrom 1-3 mm. Some of these smaller colonies can be darker in color thanthe rest of the colony population. Colonies edges are entire; but somecolonies will show irregular edges. This becomes typical after 3-4weeks. Colonies are convex to slightly umbonate. Color is red orange,darker at the raised center. Colony finish is matt. Where crowded somecolonies appear wrinkled, especially on older plates. After 3-4 weekscolony color is dark red. Lighter colonies, yellow to orange, can beoccasionally seen in lawns of cells. These lawns can have a grainyappearance.

UBV-AX2: Well isolated colonies are 4-5 mm in diameter. Some colony sizeheterogeneity is present, with smaller colonies occasionally seen.Colony edges are entire. Colonies are convex to slightly umbonate andglossy in appearance. Color is red-orange, darker at the raised centers,especially where crowded. Occasional irregularities can be seen at somecolony edges. After 3-4 weeks colonies are still glossy and dark red.Lawns of cells remain smooth and glossy. The lack of lighter coloredcolonies indicates that the genes for pigmentation in this strain arevery stable.

UBV-AX3: Colony morphology can be heterogeneous, especially after 6 daysgrowth in glucose/yeast extract broth. After 10 days on glucose/yeastextract plates, the colonies range in size from 1.5 to 3 mm in diameter.Color ranges from red to orange. Smaller colonies are typically darkerred than the larger colonies.

UBV-AX4: After two weeks on glucose/yeast extract plates, colonies are2-3 mm in diameter. The colony edges are entire, although a small numberof colonies may show scalloped edges. Colony color is a dark red-orange.The colonies are glossy, and have a conical profile, especially wherecrowded. After 3 weeks, the colony profile shows flattening at the base.The color of the colony center is darker red than the perimeter. Colonyedges remain entire.

EXAMPLE 4 Strain Description: Microscopic Appearance

Microscopic appearance of cells were observed on the novel strains grownin 2% glucose, 0.5% Tastone^(tm) -154 for 6 days.

UBV-AX1 (FIGS. 2 and 3): Cells are single or in pairs with occasionalshort chains. Cells are ellipsoid to oviform. Cells are reddish-tan.Some cells are devoid of cytoplasm with lipid droplets. Cells withgranular, slightly pigmented forms are seen. Some pleomorphic shapes arealso seen. Occasional apiculate shaped cells are present.

UBV-AX2 (FIGS. 4 and 5): Cells are single or in pairs. Cells with twobuds at the same end of a mother cell are common. Cells are oblateellipsoidal to globose. Many cells are obviously pigmented reddishbrown. Cells with granular appearing, pigmented cytoplasm are fairlycommon. Occasional enlarged, deeply pigmented, rounded"chlamydospore-like" structures are seen. The structures lack thethickened cell walls of chlamydospores.

UBV-AX3 (FIGS. 6 and 7): Cells are single, in pairs, short chains orsmall clumps of 3 to 6 cells. Pleomorphic forms are seen. Many cells areobviously pigmented. The cytoplasm in these cells appear granular.

UBV-AX4 (FIGS. 8 and 9): Cells are single or in pairs or short chains.Pleomorphic forms are seen. Some cells have reddish-brown granularcytoplasm. Some cells appear to have red-crystalline structures present.Lipid droplets are very obvious in some cells.

EXAMPLE 5 Strain Description: Cell Sizes

Table 4 shows cell sizes of the novel strains which were grown in 2%glucose and 0.5% Tastone^(tm) -154 for 6 days.

                  TABLE 4                                                         ______________________________________                                        Cell Sizes of Certain Phaffia Strains                                         Strain      Cell Size Range (μm)                                           ______________________________________                                        UBV-AX1     4.2 × 6.3 to 8.4 × 12.6                               UBV-AX2     4.2 × 5.3 to 9.5 × 10.5                               UBV-AX3     4.2 × 6.3 to 9.4 × 11.5                               UBV-AX4     4.2 × 5.2 to 9.4 × 10.4                               ______________________________________                                    

EXAMPLE 6 Enhancement of Astaxanthin Production by Exposure to LowIntensity Light

Table 5 reports that darkness is inhibitory to pigment production inshake flasks, Phaffia was grown in shake flasks with 2% glucose and 0.5%yeast extract at 200 rpm at 21 C. for six days.

                  TABLE 5                                                         ______________________________________                                        Enhancement of Astaxanthin Production                                         by Exposure to Low Intensity Light                                                       Astaxanthin (μg/ml culture broth)                               Strain       Continuous 10 ft-C Light                                                                      Dark                                             ______________________________________                                        UBV-AX1      30.1            19.2                                             UBV-AX2      43.8            17.3                                             UBV-AX3      41.6            16.1                                             ______________________________________                                    

EXAMPLE 7 Hydrolyzed Corn Syrup

Hydrolysed corn syrup (DE=95) and a partly hydrolysed corn syrup (DE=63)are mixed to produce a feed material which contains glucose andsignificant levels of various higher sugars such as maltose, maltotrioseand higher polymerized sugars. These sugars or polysaccharides are notmetabolized until the glucose is depleted. A 75:25 mixture of these twocorn syrups produces a feed of about 78% glucose and 10% maltose (aboutDE=87).

The data in Table 6 shows that UBV-AX1 produces significantly higherlevels of astaxanthin in a 20 l fermentor with a 75:25 mixture of ahydrolysed corn syrup (DE=95) and a partly hydrolysed corn syrup (DE=63)than with a hydrolyzed corn syrup (DE=95) alone.

                  TABLE 6                                                         ______________________________________                                        Astaxanthin Production Levels                                                 with DE=87 and DE=95 Corn Syrup                                               Feed          Yeast Solids                                                                             Astaxanthin                                          Corn Syrup    %          (μg/g dys*)                                       ______________________________________                                        DE=87         5.9        6,712                                                DE=95         5.9        5,892                                                ______________________________________                                         *Dry Yeast Solids                                                        

EXAMPLE 8 Glycerol Effect on Astaxanthin Production During Maturation

For most Phaffia strains astaxanthin synthesis continues after growthhas stopped. Astaxanthin is therefore considered by some to be asecondary metabolite in Phaffia. We have found that the addition ofglycerol to Phaffia stimulates carotenoid synthesis during thenon-growth phase after the primary carbon source (glucose) has beenutilized. HPLC analysis indicates that if glucose and glycerol arepresent together, the glucose is preferentially utilized and theglycerol is used only after glucose depletion. As seen in the followingtables, inclusion of glycerol along with glucose greatly enhances theastaxanthin yield of our Phaffia strains. These strains grow very poorlyif glycerol is the only carbon source.

Table 7 shows that the astaxanthin production level of Phaffia rhodozymais greatly increased by glycerol in shake flasks with 2% glucose and0.5% yeast extract in continuous low intensity light for six days.

                  TABLE 7                                                         ______________________________________                                        Glycerol Effect on Astaxanthin Production                                     in Shake Flasks                                                                        Astaxanthin (μ/ml culture broth)                                  Strain     Without Glycerol                                                                           With 1% Glycerol                                      ______________________________________                                        UBV-AX1    30.0         37.6                                                  UBV-AX2    42.8         49.2                                                  UBV-AX3    54.2         71.3                                                  UBV-AX4    42.0         56.7                                                  ______________________________________                                    

EXAMPLE 9 Slow Feeding During Maturation

The data of Table 8 shows the effect on maturation with and without acontinued feed of the energy source. Fermentations were conducted in 20l Chemap fermentors with UBV-AX1 and the standard fermentation formatsubstantially as described above. In Case 1, the fermentation was endedas the growth rate of cells declined. In Case 2, feeding of the energysource was terminated as cell growth rate declined and the cells wereallowed to mature for 72 hours. In Case 3, the feed rate of the energysource was reduced to 25% of the maximum feed rate as the yeast growthrate declined and the cells were allowed to mature for 72 hours withslow feeding.

                  TABLE 8                                                         ______________________________________                                        The Effect of Slow Feed During Maturation Phase                               on Astaxanthin Production Levels                                                                    Yeast    Astaxanthin (μg/ml                          Case Feed during Maturation                                                                         Solids % fermentation broth)                            ______________________________________                                        1    No maturation    7.0      175                                            2    Maturation without feed                                                                        5.9      362                                            3    Maturation with slow feed                                                                      7.9      561                                            ______________________________________                                    

EXAMPLE 10 Evaluation of the Novel Strains as a Source of Pigment forSalmonids

This example demonstrates that the novel strains of Phaffia rhodozymapigment salmonids flesh effectively when supplied in feed as anadditive. This example also shows that the strains of this invention donot require disruption to make astaxanthin available to salmonids(Binkowsky, Sedmak and Jolly. 1993. Aquaculture Magaine. March/April:54-59, which is incorporated herein by reference).

The Phaffia strain was grown in a 2,000 l fermentor in a mannersubstantially described as above. Cells were concentrated to 15-22%solids by centrifugation and dried. The feed was processed by ZeiglerBros. Inc., Gardners, Pa. The novel Phaffia rhodozyma or syntheticastaxanthin (5% Carophyll Pink, Hoffmann-LaRoche) were incorporated intotheir #1/8 Trout Grower pelleted food.

Rainbow trout (Onchorhynchus mykiss, Shasta strain) were obtained from alocal commercial trout grower. After acclimation to laboratoryconditions and an experimental control diet, the trout were moved intoseparate experimental tanks (28 fish per tank). The experimental tanksheld approximately 250 liters of water (76 centimeter (cm) diameter; 56cm standpipe) and had an average flow rate of 6.5 liters of water perminute.

Collectively, the procedures and diets employed in the experiments weredesigned to result in near-optimal growth of trout at 10 C., theapproximate temperature at which most commercially-produced trout areraised. By the end of the experiment, the remaining trout wereapproximately market size.

At 4, 8 and 12 weeks, 6 fish per tank were randomly removed to determinegrowth rates and pigment levels. The fish were stunned by a blow to thehead; total length measured; weight after blotting dry determined; andthen each fish was cut across the isthmus severing the ventral aorta.The fish were allowed to bleed out in cool water and then two skin-onfillets were taken from each fish. With the information acquired fromeach sampling, tank biomass was recalculated and food rations adjustedso that each tank received 1.5% of its estimated biomass in food perday.

The fillets were processed to determine carotenoid content per wetweight of flesh. About 15 g of flesh pooled from various portions of afillet were homogenized and 0.2 g samples of homogenized flesh extractedwith 1 ml of acetone for 30 minutes at room temperature to release theflesh carotenoids. The carotenoids were then partitioned intohexanes:ethyl acetate (1:1 by volume) and the total carotenoid andastaxanthin content were determined as described above in the sectionentitled PIGMENT EXTRACTION AND ASTAXANTHIN ANALYSIS.

Pellets of food were crushed with a mortar and pestle. An accuratelyweighed portion (0.05 g) of the crushed pellets were treated withdimethylsulfoxide (DMSO) for 30 minutes at room temperature to extractthe carotenoids. The DMSO extracted carotenoids were then quantified asdescribed above in the section entitled PIGMENT EXTRACTION ANDASTAXANTHIN ANALYSIS. This procedure was used for feed analysisthroughout the experimental trials.

The growth and pigmentation of rainbow trout that were fed dietscontaining our novel Phaffia yeast (one whole cells, the other milled ordisrupted cells) were compared both to rainbow trout fed an unpigmenteddiet and to rainbow trout fed a diet containing synthetic astaxanthin.

As seen in FIG. 10, the weight gain of all four groups of fish wascomparable with fish growing from approximately 240 g to 380 g duringthe 84 day trial period. This study indicates that whole or disruptedPhaffia yeast added to the diet at the above level gives the same orbetter palatability and digestibility as the control fish food. Grossanatomical examination of fish at 84 days indicated that there were nodifferences between the four treatment groups.

The flesh carotenoid content of rainbow trout fed the diet devoid ofastaxanthin (Diet D) was the same low level at 0 and 84 days of feedingindicating that the base diet for these studies was indeed devoid of anycarotenoid that might be deposited in the fish flesh. After 84 days offeeding, the flesh carotenoid content of the Phaffia and syntheticastaxanthin fed fish were the same (FIG. 11). All four groups of fishcolored at comparable rates during the 84 day trial period.

EXAMPLE 11 Evaluation of a Novel Formulation of Phaffia Product forPigmenting Salmonids

This example demonstrates that a formulation of Phaffia cells blendedwith ethoxyquin, lecithin and safflower oil increases astaxanthindeposition in salmonid fish flesh.

Phaffia was grown in a 2,000 l fermentor in a manner as substantiallydescribed above. Cells were concentrated to 15-22% solids bycentrifugation and dried. Ethoxyquin, lecithin and safflower oil wereadded to the yeast cream prior to drying. The feed was processed byZeigler Bros. Inc., Gardners, Pa. The treated and untreated Phaffia wereincorporated into their #1/8 Trout Grower pelleted food.

Rainbow trout (Onchorhynchus mykiss, Shasta strain) were obtained from alocal commercial trout grower. After acclimation to laboratoryconditions and an experimental control diet, the trout were moved intoseparate experimental tanks (14 fish per tank). The experimental tanksheld approximately 650 l of water (120 cm diameter; 56 cm standpipe) andhad an average flow rate of 11 liters of water per minute.

Collectively, the procedures and diets employed in the experiments weredesigned to result in near-optimal growth of trout at 10 to 12 C., theapproximate temperature at which most commercially-produced trout areraised. By the end of the experiment, the trout had grown from anaverage 300 g to an average 650 g. Fifteen fish were randomly sampled todetermine base line weight, length and flesh color data beforeseparating fish into experimental tanks. At 63 days 10 fish per tank andat 93 days 14 fish per tank were randomly removed to determine growthrates and pigment levels in the same manner as that described in Example10. Similarly, the procedures of Example 10 were used to process thefillets (to determine carotenoid content per wet weight of flesh), andthe pellets of food.

The growth and pigmentation of rainbow trout fed diets containingPhaffia yeast with and without lecithin and safflower oil were compared.Diet A contained Phaffia treated with 2,000 ppm ethoxyquin. Diet Bcontained Phaffia treated with 2,000 ppm ethoxyquin and 2.5% soylecithin. Diet C contained Phaffia treated with 2,000 ppm ethoxyquin,2.5% soy lecithin and 2.5% safflower oil.

                  TABLE 9                                                         ______________________________________                                        Pigmentation of Fish Flesh at 93 Days                                                    Astaxanthin in Flesh                                               Diet       in Feed (ppm)                                                                             (ppm/wet wt)                                           ______________________________________                                        A          49          2.01 ± 1.32                                         B          49          3.02 ± 1.87                                         C          48          4.50 ± 1.40                                         ______________________________________                                    

As seen from the data in Table 9, after 93 days of feeding, fish fed thediet containing Phaffia treated with ethoxyquin, soy lecithin andsafflower oil were pigmented best.

Although the invention has been described in considerable detail throughthe preceding examples, such detail is for the purpose of illustration.Many variations and modifications can be made by one skilled in the artwithout departing from the spirit and scope of the invention asdescribed in the appended claims.

What is claimed is:
 1. A strain of Phaffia rhodozyma selected from thegroup consisting of Phaffia rhodozyma ATCC-74218, ATCC-74219,ATCC-74220, ATCC-74221 and mutants thereof which retain theastaxanthin-producing capability.
 2. The strain of claim 1 wherein thestrain is Phaffia rhodozyma ATCC-74218.
 3. The strain of claim 1 whereinthe strain is Phaffia rhodozyma ATCC-74219.
 4. The strain of claim 1wherein the strain is Phaffia rhodozyma ATCC-74220.
 5. The strain ofclaim 1 wherein the strain is Phaffia rhodozyma ATCC-74221.